1. Field of The Invention
The present invention relates generally to energy absorbers and energy absorption systems, and more particularly to shock and vibration energy absorption systems for vehicle seats for mitigating occupant injury due to extreme vehicle movement (e.g., during a vehicle shock event), and/or for mitigating vibration experienced by an occupant of the vehicle seat during normal vehicle operating conditions.
2. Discussion of the Related Art
The minimization of shock load-induced injury is an important issue in seat suspension design. Occupant spinal and pelvic injuries, for example, may result from harsh vertical/crash landings of aircraft, as well as from vertical shock of land and marine vehicles. The severity of resulting spinal, pelvic, or other injuries may be considerably minimized if vehicles are equipped with crashworthy seat designs. A seat suspension system can be used to mitigate the vertical shock loads that are transmitted from the base of the vehicle (or extension thereof), and imparted into the human body. The attenuation of vertical impact forces in vehicle mishaps is one of the prime factors in determining survivability.
Energy absorbers, also known as energy attenuators or load limiters, are a key component of crashworthy seat designs. Energy-absorbing crew seats for helicopter applications, for example, have made significant improvements in helicopter crash survival. Early crashworthy crew seats used fixed-load energy absorbers (FLEAs) to limit the load on an occupant's spine. One drawback associated with these FLEAs, however, is that they were not adjustable and stroked at a factory-established, constant load throughout their entire operating range. Variable load energy absorbers (VLEAs) were designed to address this drawback.
A VLEA enables an occupant to manually adjust the constant stroking load by setting a control (e.g., a dial) to the occupant's weight. The load increases for large occupants, for example, taking advantage of their greater spinal load tolerance to reduce the stroked distance. By contrast, the load decreases for smaller occupants to reduce the risk of injury to their weaker spines. A VLEA enables a seat to deliver the same low-injury risk regardless of occupant weight. VLEAs were developed with a provision so that a wide range of occupants would have equal protection in a crash. An energy absorber load is selected that is proportional to the occupant's weight so that each occupant will experience similar acceleration and use similar stroking space in a crash.
Both FLEAs and VLEAs are known as fixed profile energy absorbers (FPEAs) because they have a constant load-stroke curve. One drawback associated with FPEAs is that they are passive, meaning that they cannot adapt their energy absorption or stroking profiles as a function of occupant weight, or as a function of real-time environmental measurements such as a crash velocity, vibration or shock load. These variables are essential if vibrations and/or impact energy is to be absorbed most efficiently. Seat suspension systems that utilize FPEAs suffer from these and other drawbacks.
In their related U.S. Pat. Nos. 7,878,312 and 7,822,522, the inventors therein describe several variations of an adaptive energy absorption system for a vehicle seat utilizing an adaptive energy absorber or variable profile energy absorber (VPEA) for mitigating injury due to extreme vehicle movement (e.g., during a vehicle shock event), and/or for mitigating vibration, over a wide range of occupant weights and load levels. The adaptive energy absorption system comprises a VPEA, a controller (e.g., a single-mode or multi-mode controller), and one or more sensors for indication and/or measurement of surrounding stimuli, including extreme motion “shock events.”The VPEA responds to changing environmental stimuli such as occupant weight, occupant attitude, load level, or other stimuli, to effectively mitigate loads into the occupant's body. During normal operating conditions, for example, the VPEA may be automatically adjusted in real-time to minimize occupant motion based upon a known occupant weight (e.g., automatically sensed or manually adjusted) and known vibration levels (e.g., from sensors). Limiting seat motion provides the advantages of enhancing comfort and reducing fatigue for the occupant of the vehicle seat. During an extreme motion event (e.g., a shock event), motion sensors may trigger the controller into a secondary mode, wherein the VPEA may be automatically adjusted to keep body loads (pelvic loads, spinal loads, etc.) within acceptable levels. An optional fixed profile energy absorber FPEA may also be included, the variable profile energy absorber and the fixed profile energy absorber configured to be in series to mitigate vibration and shock. These disclosed embodiments provide the capability to adapt to tune the system to the harshness of each particular event and adapt to varying shock input levels in real-time using environmental measurements. The co-pending applications provide an advantage over conventional seat energy absorption systems which tend to be tuned for a fixed shock level (thus, not optimally controlling body loads for other shock levels).
VPEA is herein defined as any suitable device used to absorb energy by providing a controlled resistive force applied over a deformation distance without significant elastic rebound, and for which the controlled resistive force can be continuously adjusted over that over a deformation distance. Suitable VPEAs may comprise any of an active valve damper, a magnetorheological fluid damper, an electrorheological fluid damper, a magnetic energy absorber, and a servo-hydraulic actuator. Active valve dampers are pneumatic or hydraulic cylinders that rely on internal valving changes to automatically adjust their damping effect. Active valve dampers with electrically controlled damping constants are known in the art, and typically use variable valve orifices to adjust the damping force.
A magnetorheological fluid damper is a damper filled with magnetorheological fluid, which viscosity is controlled by a magnetic field, usually using an electromagnet. This allows the damping characteristics of the shock absorber to be continuously controlled by varying the power of the electromagnet. Magnetorheological fluid dampers are likewise known in the art and available, for example, from the Lord Corporation of Cary, N.C.
An electrorheological fluid damper is a damper filled with electrorheological fluid, which viscosity is controlled by electric an electric field applied to the fluid. Fludicon GmbH markets various standard and custom electrorheological fluid dampers.
By way of background, ER and MR fluids possess the ability to change properties when electric or magnetic fields are applied there across, respectively. This change is mainly manifested as a substantial increase in dynamic yield stress, or apparent viscosity, of the fluid. ER and MR fluids exhibit nonlinear effects due to applied field, applied loads, strain amplitude, and frequency of excitation in dynamic displacement conditions.
The application of ER & MR fluids to the valve of a damper in the presence of a controllable electric/magnetic field results in the semi-active device known as an ER & MR damper, respectively. A variety of magnetic energy absorbers have been developed and are known in the art including cylindrical-type electromagnetic actuators that use magnetic fields from electromagnets to apply damping to a structure.
A servo-hydraulic actuator employs a hydraulic cylinder-type actuator controlled by a servo motor.
The VPEA responds to changing environmental stimuli such as occupant weight, occupant attitude, load level, or other stimuli, to effectively mitigate loads into the occupant's body. During normal operating conditions, for example, the VPEA may be automatically adjusted in real-time to minimize occupant motion based upon a known occupant weight (e.g., automatically sensed or manually adjusted) and known vibration levels (e.g., from sensors). Limiting seat motion provides the advantages of enhancing comfort and reducing fatigue for the occupant of the vehicle seat. During an extreme motion event (e.g., a shock event), motion sensors may trigger the controller to automatically adjust the VPEA to keep body loads (pelvic loads, spinal loads, etc.) within acceptable levels. In combination with the VPEA, an optional fixed profile energy absorber FPEA may also be included, the VPEA and FPEA being configured in series to mitigate vibration and shock. These disclosed embodiments provide the capability to adapt to tune the system to the harshness of each particular event and adapt to varying shock input levels in real-time using environmental measurements. The co-pending applications provide an advantage over conventional seat energy absorption systems which tend to be tuned for a fixed shock level (thus, not optimally controlling body loads for other shock levels).
The present invention expands the concept by providing the capability of responding to more than one (e.g., repetitive) shock event. The general system components, architecture, and function are the similar and the present system likewise employs an adaptive seat energy absorption system that utilizes a variable profile energy absorber (VPEA) to prevent bodily injury during a shock event. However, the present system employs a dual mode operation. When operating in primary mode during normal operating conditions (non-shock event) the system functions to minimize occupant motion based upon a known occupant weight (e.g., automatically sensed or manually adjusted) and known vibration levels (e.g., from sensors). Limiting seat motion provides the advantages of enhancing comfort and reducing fatigue for the occupant of the vehicle seat. In addition, the present system automatically switches to and functions in secondary mode during severe (shock event) operation, and automatically adjusts in real-time to keep loads transmitted to the occupant's body below acceptable injury threshold levels, and can recover to perform said function for multiple shock events.